Clad porous metal sheets



April 13, 1965 H. A. KUCHEK 3,177,574

GLAD POROUS METAL SHEETS Filed 001;- 1961 INVENTOR. Henry A. KuC/nfk *gwmm flTTORNEY United States Patent 3,177,574 CLAD POROUS METAL SHEETS Henry A. Kuchek, Auburn, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Oct. 9, 1961, Ser. No. 143,622 2 Claims. (Cl. 29-423) This invention relates to a flat, clad, .porous article of manufacture and a method for producing said article.

The accompanying drawing, forming a part of this specification, is an isometric view partially in section of the final product of this invention.

The end product of the present invention has a thin dense metal exterior surface 2 called a cladding and a porous metal core 3. Core metal 3 is of the nature of a metal sponge and has pores which are interconnected.

The article of this invention is particularly useful where a light rigid plate is desirable, and where the article is used for storage of liquids as well as a structural member in an assembly, is. aircraft wings used also to store fuel, but the invention is not thus limited. In use for liquid storage, the article is stronger than a plain tank of simailar dimension and capacity, and also shows the advantage of inhibiting or damping rapid motion or surge of the liquid when the article is moved suddenly.

Preparation of the article of this invention is begun by casting a suitable metal or metal alloy, preferably aluminum or aluminum alloy containing at least 75 percent aluminum, into a mold filled with a water soluble salt in granular form. Suitable sizes of granular salt are those as small as will pass a 100 mesh screen and those as large as will allow sufficient metal to remain to result in a self-supporting article, sometimes as much as an inch in diameter or greater, depending on the size of the mold. While the shape of the salt will preferably be equiaxed, oblong or irregularly shaped pieces may be employed. The salt must have a melting temperature higher than the temperature at which the metal or metal alloy is to be cast, must be insoluble in the liquid metal or metal alloy, must not be so strongly or rapidly corrosive in aqueous media toward the metal or metal alloy as to destroy the metal or metal alloy in the time required to leach the salt from the casting, and must not be reducible in aqueous media by the cast metal or metal alloy so as to leave an undesired metal residue in the porous core. Salts usable in the method of this invention are, for example, sodium chloride, potassium chloride, barium chloride, and the like which meet the requirements described above.

By proper selection of the salt to be employed in the casting step, keeping in mind the requisite properties described above, the practice of this invention may be extended to any rollable metal or metal alloy, as for example, lead, magnesium, aluminum, tin, copper, and their alloys. 7

Prior to casting, the salt-filled mold is preheated to a temperature near the melting point of the metal or metal alloy. The molten metal is then poured into the hot salt-filled mold. Preheating the mold ensures a good penetration by the metal of the spaces between the salt grains and is particularly desirable if the salt grains are of a very small size.

After solidification the metal-salt casting is removed from the mold. By machining or other means, the casting is given a shape suitable for the core of the article. Thecastin-g is then heated to a suitable temperature and placedcentrally in a mold so as to form a core. The space between the core and the walls of the mold is the same as the thickness desired for the dense metal cladding prior to rolling. Metal of the same general composition as in the metal-salt casting is cast into the mold so as to fill the space between the casting and the walls of the mold. The mold used in this step is generally of a square or rectangular cross-sectional shape. If another shape is used, rolling will form the article so that the major external surfaces are generally parallel.

0n completion of the preparatory steps described above, the soaformed article, hereinafter referred to as a billet, is preheated to a temperature suitable for rolling operations. After preheating, the billet is rolled in a rolling mill or some similar device until the billet has acquired the desired dimensions in overall size and dense metal coating thickness. Salt is retained in the core to prevent collapse of the pore walls during rolling.

Removal of the salt from the core of the article is then accomplished by leaching with water. The leaching step essentially completes the process. The resultant article has a porous core having relatively uniform interconnected pores, said core being surrounded by a dense metal cladding which is bonded to the core metal so that a final article of essentially unitary structure is obtained.

The following example is set forth to illustrate, but not to limit, this invention.

Example A cylindrical mold having a diameter of 3 inches and a depth of 8 inches was prepared by filling it with sodium chloride granules of an 8-12 mesh size, U.S. sieve series. The sodium chloride containing mold was preheated to about 700 C. An aluminum alloy having the nominal composition of 5 percent silicon, balance aluminum was cast into the mold at a temperature of about 760 C.

After. solidification, the metal-salt cylinder was re moved from the mold and cut to a rectangular shape of the dimensions 1 /2 x 3 x 3 /2 inches. A steel rod of A inch diameter was threaded into one end of the casting. The casting with the steel rod attached was heated to about 500 C. and centrally placed in a 2 x 4 x 8 inch book mold. The steel rod was used to support the metalsalt casting in its position in the mold as a core.

Aluminum alloy, having the nominal composition 5 percent silicon, balance aluminum, was cast at about 760 C. into the book mold so as to completely surround the metal-salt core. After solidification of the composite casting, the steel rod was removed.

To prepare the billet thus formed for a rolling operation, it was heated to about 315 C. in an electric furnace. Rolling was accomplished on an 8 inch rolling mill having steam heated rolls using a speed of about feet per minute. The billet was reduced in thickness with about a 10 percent reduction per pass. During the rolling operation, the billet was periodically reheated to about 315 C. The billet was finally reduced to a thickness of about /4 inch. v

The dense metal ends were cut from the product of the rolling operation, to expose the salt-filled core, and the salt was leached from the pores with water. It is necessary to expose the core in some manner in order to allow water to reach and dissolve the salt in the leaching operation.

Examination of the article indicated a good metallurgical bond between the core metal and the dense metal cladding, and good communication between the pores in the core. Each ml. of core volume was found to contain about 65 m1. of pore volume, useful for storage of that volume of inert liquid.

Various modifications may be made in the present invention without departing from the spirit or scope thereof, audit is to be understood that I limit myself only as defined in the appended claims.

Iilaimi v i 1. Themcthod pf produciii'g a generally flat, .reetangular article which comprisesv casting a metalinto a mold,

solidificatiqn; placing said casting aSI-he core in,a; se'c nd mold, casting metal i nto, the; second moldy'sd a slto' su rround the core; subjecting the ar ticle thus formed "toja" rolling process; andlemoyingjthe salt b'y leaching,

filled with water soluble salt granules which have, a meltpoint -abqve ,the lempfatupe at which -the metal 'is" l ar zi'rticle which comprises casting a"me/telQfffthfilags of aluminurn-and aluminum alloys'intjq'a mold filled with V water' Soluble, salt granulels which hgvei meltingpoiiit above the temperature at Whichfthe inetaLjs cast; ramm- :ing the salt metal cqsting from the-mold after solidifica- '7 tion,-p1acing said casting (a; the; corel-iua Second, mold,

casting a metal of ,the class' of aluminum and aluminum V allc'iy s iiito the manam' c ild sofas to' surrciiihdltlie 'cre,

subjecting ,the article :thus formed to a rolling process,

and e'mov ing the salt by leaching.

V, V' R eiereiices Cit egi'b y th e Baikminer,

IT DQSTATES 'PAT NTS FOREIGN 'PATENTS 7 MICHAEL' 'V;'BRlNPISL fiimkzi y-Eiahzirien 1- 

1. THE METHOD OF PRODUCING A GENERALLY FLAT, RECTANGULAR ARTICLE WHICH COMPRISES CASTING A METAL INTO A MOLD FILLED WITH WATER SOLUBLE SALT GRANULES WHICH HAVE A MELTING POINT ABOVE THE TEMPERATURE AT WHICH THE METAL IS CAST, REMOVING THE SALT-METAL CASTING FROM THE MOLD AFTER SOLIDIFICATION, PLACING SAID CASTING AS THE CORE IN A SECOND MOLD, CASTING METAL INTO THE SECOND MOLD SO AS TO SUR- 